Many types of elastic materials are used in daily necessities such as underwear and socks, in the waist and crotch of disposable diapers, in elastic bandages, and in the sleeve cuffs of surgical gowns. They are used to strengthen and improve the adhesion of these products to the human body. Materials commonly used in these capacities are elastic bodies such as natural, synthetic, or polyurethane rubber, in the form of filaments, foam, film, or netting, and covered in cloth, non-woven fabric, or a filamentous covering to prevent the elastic body from coming in direct contact with the skin.
The best known expandable material is a pleated elastic complex formed by elongating the elastic body, keeping it elongated while bonding the covering material to it through heat, ultrasound waves, or an adhesive agent, then releasing the tension in the bonded body. The elastic body used in the waist and crotch of disposable diapers currently on the market is this type of material.
Another common expandable material is an elastic complex. This is formed by using ultrasound waves or an adhesive agent to bond a potential elastic body having characteristics of heat contractibility with an unelongatable material. The bonded body is then processed in its tension-free state within a hot ambient atmosphere and the potential elastic body contracted.
Additionally, JPA Sho 59-5990 disclosed another technique for obtaining an elastic complex. The technique involves partially, or discontinuously, bonding a net-form elastic body in a relaxed state with an unelongatable backing material having an elongatability relatively lower than film containing PE and EVA. The partially bonded body is elongated to the necessary extent under high tension, within the allowable elongation range of the backing material. Next, a larger permanent distortion is made in the non-bonded portion of the backing than is made in the bonded portion. The tension is then released from this elongated bonded body to return the elastic body to a relaxed state. In this manner, the elastic complex possesses expandability. It has been noted that elastic complexes made through the three conventional techniques described above all have the disadvantage of insufficient suppleness and comfort against the skin. These complexes are thus unsatisfactory materials for products such as diapers and sanitary napkins which stay in contact with the skin for long periods of time.
In general, liquid impermeability and gas permeability, or breathability, are opposing conditions. Enhancing the one results in diminishing the other. Conventional techniques have not created a material which can satisfy both of these conditions simultaneously. Existing products are also unsatisfactory from the viewpoint of industrial manufacturing, in which the ease and low cost of manufacturing are important elements.
Ideally, to solve these problems without causing a deterioration in absorption or other types of performance and without causing a price increase, the backing at the edges of the waist and the elastic body should not be in direct contact, allowing full use of the elastic body's expansion strength. One method of achieving this is to use a floating structure, suspending the elastic body from the edge backing in a floating fashion. In forming the floating structure, there should be as few as possible points of bonding between the backing material and the elastic body, but a certain number will be required to give the structure an even distribution of elasticity.
The purpose of this invention is to provide a sheet elastic complex which has sufficient elasticity for sanitary products such as diapers and which does not allow for any essential diminishment in liquid absorption performance, as the elastic body is attached in such a way as to hold a floating structure.